BIS(2-AMINOMETHYLPYRIDINE) COMPLEXES OF CR(III) AND CO(III)

Of the five isomers possible for [MX2(ampy)(2)]Y, two each (both cis) for M = Co(III), M = Cr(III) have been fully characterised by single c rystal X-ray structural analysis. cis-alpha-[CoCl2(ampy)(2)] Cl . H2O (1) (orthorhombic, Pccn, a = 13.235(3), b = 13.273(3), c =10.800(2) An gstrom, V = 1897.2(7) Angstrom(3), Z = 4) and cis-alpha-[CrCl2(ampy)(2 )] ClO4. H2O (2) (orthorhombic, Pccn, a = 13.038(2), b = 13.703(2), c = 11.204(3) Angstrom, V = 2001.7(7) Angstrom(3), Z = 4) have the coord inated chloro ligands trans to the NH2(CH2)(2) arms of the ampy ligand whereas for cis-beta-[CoCl2(ampy)(2)] ClO4 (3) (triclinic, P (1) over bar, a = 8,2890(10), b = 11.7887(14), c = 17.863(3) Angstrom, alpha = 85.407(10), beta = 77.363(10), gamma = 88.268(7)degrees V = 1697.6(4) Angstrom(3), Z = 4) and cis-beta-[CrCl2(ampy)(2)] ClO4 (4) (triclinic , P (1) over bar, a = 7.2170(10), b = 10.711(2), c = 12.423(2) Angstro m, alpha = 106.820(10), beta = 101.270(10), gamma = 101.980(10)degrees , V = 865.1(2) Angstrom(3), Z = 2), the coordination geometry of one o f the ampy ligands is reversed with respect to the alpha-isomer. In th e Co(III) series we also have evidence for one of the trans-isomers (N H2(CH2)(2)-arms trans to each other) in trans-[CoCl(NO2) (ampy)(2)](2) ZnCl4. 2H(2)O and for the existence of the gamma-cis-[CoCl2(ampy)(2)]C l (both chloro ligands trans to the py-ends of the diamine) isomer. Th e rate of the loss of the first chloro ligand from cis-alpha and cis-b eta-[MCl2(ampy)(2)](+) has been measured in 0.1 M HNO3. Kinetic parame ters (25 degrees C) are k(H)(alpha-Co) = 3.39 x 10(-5) s(-1), Delta H- not equal = 86.8 kJ mol(-1), Delta S-not equal = - 39 J K-1 mol(-1); k (H)(alpha-Cr) = 7.78 x 10(-6), Delta H-not equal = 83.5, Delta S-not e qual = - 62; k(H)(beta-Co) = 2.18 x 10(-5), Delta H-not equal = 85.5, Delta S-not equal = - 51; k(H)(beta-Cr) = 1.95 x 10(-5), Delta H-not e qual = 81.8, Delta S-not equal = - 61. (C) 1998 Elsevier Science S.A. All rights reserved.